Method to make single-layer pet bottles with high barrier and improved clarity

ABSTRACT

The present invention comprises a blend of polyester and a partially aromatic polyamide with an ionic compatibilizer and a cobalt salt. This blend can be processed into a container that has both active and passive oxygen barrier and carbon dioxide barrier properties at an improved color and clarity than containers known in the art. The partially aromatic polyamide is preferably meta-xylylene adipamide. The ionic compatibilizer is preferably 5-sodiumsulfoisophthalic acid or 5-zincsulfoisophthalic acid, or their dialkyl esters such as the dimethyl ester (SIM) and glycol ester (SIPEG). The cobalt salt is selected form the class of cobalt acetate, cobalt carbonate, cobalt chloride, cobalt hydroxide, cobalt naphthenate, cobalt oleate, cobalt linoleate, cobalt octoate, cobalt stearate, cobalt nitrate, cobalt phosphate, cobalt sulfate, cobalt (ethylene glycolate), or mixtures of two or more of these. The partially aromatic polyamide is present in a range from about 1 to about 10 wt. % of said composition. The ionic compatibilizer is present in a range from about 0.1 to about 2.0 mol-% of said composition. The cobalt salt is present in a range from about 20 to about 500 ppm of said composition.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.10/569,614 filed Feb. 24, 2006; which is a 371 of PCT/US04/25257 filedAug. 5, 2004; which claims benefit of priority from U.S. ProvisionalApplication Ser. No. 60/498,311 filed Aug. 26, 2003.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The invention relates to compatibilized blends of polyamides inpolyesters, a method for forming such compositions, and to containersmade from such compositions. Specifically the compositions have lessyellowness than previous blends. The blends can be used as passive gasbarriers, or active oxygen scavengers with the addition of a transitionmetal catalyst.

2) Prior Art

Plastic materials have been replacing glass and metal packagingmaterials due to their lighter weight, decreased breakage compared toglass, and potentially lower cost. One major deficiency with polyestersis its relatively high gas permeability. This restricts the shelf lifeof carbonated soft drinks and oxygen sensitive materials such as beerand fruit juices.

Multilayer bottles containing a low gas permeable polymer as an innerlayer, with polyesters as the other layers, have been commercialized.Blends of these low gas permeable polymers into polyester have not beensuccessful due to haze formed by the domains in the two-phase system.The preferred polyamide is a partially aromatic polyamide containingmeta-xylylene groups, especially poly (m-xylylene adipamide), MXD6.

The MXD6 bulletin (TR No. 0009-E) from Mitsubishi Gas Chemical Company,Inc., Tokyo Japan, clearly shows that the haze of a multilayer bottlecontaining a layer of 5 wt-% MXD6 is ˜1% compared to 15% for a blend ofthe same 5 wt-%.

However, the use of partially aromatic polyamides as the low gaspermeable polymer gives an increase in the yellowness of the resultantcontainer.

U.S. Pat. No. 4,501,781 to Kushida et al. discloses a hollow blow-moldedbiaxially oriented bottle shaped container comprising a mixture ofpolyethylene terephthalate (PET) resin and a xylylene group-containingpolyamide resin. Both monolayer and multilayer containers are disclosed,but there is no information on the color of the bottles.

U.S. Pat. No. 5,650,469 to Long et al. discloses the use of aterephthalic acid based polyester blended with low levels (0.05 to 2.0wt-%) of a polyamide to reduce the acetaldehyde level of the container.These blends produced lower yellowness containers than a correspondingblend made from a dimethyl terephthalate based polyester, but are stillunsatisfactory for the higher levels required to significantly lower(decrease) the gas permeability.

U.S. Pat. Nos. 5,258,233, 5,266,413 and 5,340,884 to Mills et al.discloses a polyester composition comprising 0.05 to 2.0 wt-% of lowmolecular weight polyamide. At a 0.5 wt-% blend of MXD6 the haze of thebottle increased from 0.7 to 1.2%. No gas permeation or color data isgiven.

U.S. Pat. No. 4,837,115 to Igarashi et al. discloses a blend of aminoterminated polyamides with PET to reduce acetaldehyde levels. There wasno increase in haze with the addition of 0.5 wt-% MXD6, but at 2 wt-%the haze increased from 1.7 to 2.4%. No gas permeation or color data isgiven.

U.S. Pat. No. 6,239,233 to Bell et al. discloses a blend of acidterminated polyamides with PET that has reduced yellowness compared toamino terminated polyamides. No gas permeation data is given.

U.S. Pat. No. 6,346,307 to Al Ghatta et al. discloses the use of adianhydride of a tetracarboxylic acid to reduce the dispersed domainsize of a blend of MXD6 in PET. The examples did not give color data,but at a 10 wt-% MXD6 blend level the oxygen permeability was reducedfrom 0.53 to 0.12 ml/bottle/day/atm and the carbon dioxide permeabilitywas reduced from 18.2 to 7.02 ml/bottle/day/atm.

U.S. Pat. No. 6,444,283 to Turner et al. discloses that low molecularweight MXD6 polyamides have lower haze than higher molecular weight MXD6when blended with PET. The examples did not give color data, but at a 2wt-% MXD6 (Mitsubishi Chemical Company grade 6007) the oxygenpermeability of an oriented film was reduced from 8.1 to 5.7 cc-mil/100in²-atm-day compared to 6.1 for the low molecular weight MXD6.

U.S. Pat. No. 4,957,980 to Koyayashi et al. discloses the use of maleicanhydride grafted copolyesters to compatibilize polyester-MXD6 blends.

U.S. Pat. No. 4,499,262 to Fagerburg et al. discloses sulfo-modifiedpolyesters that give an improved rate of acetaldehyde generation and alower critical planar stretch ratio. Blends with polyamides were notdiscussed.

Japanese Pat. No. 2663578 B2 to Katsumasa et al. discloses the use of0.5 to 10 mole % 5-sulfoisophthalte copolymers as compatibilizer ofpolyester-MXD6 blends. No color data was given.

The use of a transition metal catalyst to promote oxygen scavenging inpolyamide multilayer containers, and blends with PET, has been disclosedin the following patents, for example.

U.S. Pat. Nos. 5,021,515, 5,639,815 and 5,955,527 to Cochran et al.disclose the use of a cobalt salt as the preferred transition metalcatalyst and MXD6 as the preferred polyamide. There is no data on thecolor or haze of the polyamide blends.

U.S. Pat. Nos. 5,281,360 and 5,866,649 to Hong, and U.S. Pat. No.6,288,161 to Kim discloses blends of MXD6 with PET and a cobalt saltcatalyst. There is no data on the color or haze of the polyamide blends.

U.S. Pat. No. 5,623,047 to You et al. discloses the use of a catalystcomposition containing an alkali metal acetate, preferably 30 ppm cobaltacetate to mask the yellowness in polyesters polymerized fromterephthalic acid.

US Pat. Application 2003/0134966 A1 to Kim et al. discloses the use ofcobalt octoate and xylene group-containing polyamides for use inmulti-layer extrusion blow-molding for improved clarity. Extrusionblow-molding minimizes the orientation of the polyamide domain sizecompared to injection stretch blow molding containers. No color data isgiven.

There is a need for an improved gas barrier polyester composition thatcan be injection stretch blow molded as a monolayer container that hasreduced yellowness and adequate haze. This is particularly required forcontainers that require a long shelf life, such as beer and other oxygensensitive materials. None of these patents disclose how this balance ofproperties can be achieved.

SUMMARY OF THE INVENTION

The present invention is an improvement over polyester/polyamide blendsknown in the art in that these compositions have reduced yellowness.

In the broadest sense the present invention comprises a compatibilizedblend of polyester and a partially aromatic polyamide with an ioniccompatibilizer and a cobalt salt.

The broadest scope of the present invention also comprises a containerthat has both active and passive oxygen barrier and carbon dioxidebarrier properties at an improved color and clarity than containersknown in the art.

In the broadest sense the present invention also comprises a containerin which the balance of gas barrier properties and color can beindependently balanced.

In the broadest sense the present invention is a method to blendpolyester and polyamides with an ionic compatibilizer and a cobalt salt.

The drawing is to aid those skilled in the art in understanding theinvention and is not meant to limit the scope of the invention in anymanner beyond the scope of the claims.

FIG. 1 shows a graph of the oxygen permeation rate of selected runs ofExample 3.

FIG. 2 shows a graph of the oxygen permeation rate of the runs ofExample 4.

DETAILED DESCRIPTION OF THE INVENTION

Compositions of the present invention comprise: polyester, partiallyaromatic polyamide, ionic compatibilizer, and a cobalt salt.

Generally polyesters can be prepared by one of two processes, namely:(1) the ester process and (2) the acid process. The ester process iswhere a dicarboxylic ester (such as dimethyl terephthalate) is reactedwith ethylene glycol or other diol in an ester interchange reaction.Because the reaction is reversible, it is generally necessary to removethe alcohol (methanol when dimethyl terephthalate is employed) tocompletely convert the raw materials into monomers. Certain catalystsare well known for use in the ester interchange reaction. In the past,catalytic activity was then sequestered by introducing a phosphoruscompound, for example polyphosphoric acid, at the end of the esterinterchange reaction. Primarily the ester interchange catalyst wassequestered to prevent yellowness from occurring in the polymer.

Then the monomer undergoes polycondensation and the catalyst employed inthis reaction is generally an antimony, germanium or titanium compound,or a mixture of these.

In the second method for making polyester, an acid (such as terephthalicacid) is reacted with a diol (such as ethylene glycol) by a directesterification reaction producing monomer and water. This reaction isalso reversible like the ester process and thus to drive the reaction tocompletion one must remove the water. The direct esterification stepdoes not require a catalyst. The monomer then undergoes polycondensationto form polyester just as in the ester process, and the catalyst andconditions employed are generally the same as those for the esterprocess.

For most container applications this melt phase polyester is furtherpolymerized to a higher molecular weight by a solid statepolymerization.

In summary, in the ester process there are two steps, namely: (1) anester interchange, and (2) polycondensation. In the acid process thereare also two steps, namely: (1) direct esterification, and (2)polycondensation.

Suitable polyesters are produced from the reaction of a diacid ordiester component comprising at least 65 mol-% terephthalic acid orC₁-C₄ dialkylterephthalate, preferably at least 70 mol-%, morepreferably at least 75 mol-%, even more preferably, at least 95 mol-%,and a diol component comprising at least 65% mol-% ethylene glycol,preferably at least 70 mol-%, more preferably at least 75 mol-%, evenmore preferably at least 95 mol-%. It is also preferable that the diacidcomponent is terephthalic acid and the diol component is ethyleneglycol, thereby forming polyethylene terephthalate (PET). The molepercent for all the diacid component totals 100 mol-%, and the molepercentage for all the diol component totals 100 mol-%.

Where the polyester components are modified by one or more diolcomponents other than ethylene glycol, suitable diol components of thedescribed polyester may be selected from 1,4-cyclohexandedimethanol,1,2-propanediol, 1,4-butanediol, 2,2-dimethyl-1,3-propanediol,2-methyl-1,3-propanediol (2MPDO) 1,6-hexanediol, 1,2-cyclohexanediol,1,4-cyclohexanediol, 1,2-cyclohexanedimethanol,1,3-cyclohexanedimethanol, and diols containing one or more oxygen atomsin the chain, e.g., diethylene glycol, triethylene glycol, dipropyleneglycol, tripropylene glycol or mixtures of these, and the like. Ingeneral, these diols contain 2 to 18, preferably 2 to 8 carbon atoms.Cycloaliphatic diols can be employed in their cis or trans configurationor as mixture of both forms. Preferred modifying diol components are1,4-cyclohexanedimethanol or diethylene glycol, or a mixture of these.

Where the polyester components are modified by one or more acidcomponents other than terephthalic acid, the suitable acid components(aliphatic, alicyclic, or aromatic dicarboxylic acids) of the linearpolyester may be selected, for example, from isophthalic acid,1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,succinic acid, glutaric acid, adipic acid, sebacic acid,1,12-dodecanedioic acid, 2,6-naphthalenedicarboxylic acid, bibenzoicacid, or mixtures of these and the like. In the polymer preparation, itis often preferable to use a functional acid derivative thereof such asthe dimethyl, diethyl, or dipropyl ester of the dicarboxylic acid. Theanhydrides or acid halides of these acids also may be employed wherepractical. These acid modifiers generally retard the crystallizationrate compared to terephthalic acid.

Also particularly contemplated by the present invention is a modifiedpolyester made by reacting at least 85 mol-% terephthalate from eitherterephthalic acid or dimethyl-terephthalate with any of the abovecomonomers.

In addition to polyester made from terephthalic acid (or dimethylterephthalate) and ethylene glycol, or a modified polyester as statedabove, the present invention also includes the use of 100% of anaromatic diacid such as 2,6-naphthalene dicarboxylic acid or bibenzoicacid, or their diesters, and a modified polyester made by reacting atleast 85 mol-% of the dicarboxylate from these aromatic diacids/diesterswith any of the above comonomers.

Preferably the polyamide used as the gas barrier component of the blendis selected from the group of partially aromatic polyamides is which theamide linkage contains at least one aromatic ring and a non-aromaticspecies. Preferred partially aromatic polyamides include:poly(m-xylylene adipamide); poly(hexamethylene isophthalamide);poly(hexamethylene adipamide-co-isophthalamide); poly(hexamethyleneadipamide-co-terephthalamide); poly(hexamethyleneisophthalamide-co-terephthalamide); or mixtures of two or more of these.The most preferred is poly(m-xylylene adipamide).

The preferred range of polyamide is 1 to 10% by weight of thecomposition depending on the required gas barrier required for thecontainer.

The ionic compatibilizer is preferably a copolyester containing a metalsulfonate salt group. The metal ion of the sulfonate salt may be Na+,Li+, K+, Zn++, Mn++, Ca++ and the like. The sulfonate salt group isattached to an aromatic acid nucleus such as a benzene, naphthalene,diphenyl, oxydiphenyl, sulfonyldiphenyl, or methylenediphenyl nucleus.

Preferably, the aromatic acid nucleus is sulfophthalic acid,sulfoterephthalic acid, sulfoisophthalic acid,4-sulfonaphthalene-2,7-dicarboxylic acid, and their esters. Mostpreferably, the sulfomonomer is 5-sodiumsulfoisophthalic acid or5-zincsulfoisophthalic acid and most preferably their dialkyl esterssuch as the dimethyl ester (SIM) and glycol ester (SIPEG). The preferredrange of 5-sodiumsulfoisophthalic or 5-zincsulfoisophthalic acid toreduce the haze of the container is 0.1 to 2.0 mol-%.

Suitable cobalt compounds for use with the present invention includecobalt acetate, cobalt carbonate, cobalt chloride, cobalt hydroxide,cobalt naphthenate, cobalt oleate, cobalt linoleate, cobalt octoate,cobalt stearate, cobalt nitrate, cobalt phosphate, cobalt sulfate,cobalt (ethylene glycolate), and mixtures of two or more of these, amongothers. As a transition metal catalyst for active oxygen scavenging, asalt of a long chain fatty acid is preferred, cobalt octoate or stearatebeing the most preferred. For color control of passive gas barrierblends any cobalt compound can be used, with cobalt acetate beingpreferred.

It has surprisingly been found that the ionic compatibilizer, inaddition to improving gas barrier properties and improving haze, incombination with a cobalt salt significantly reduces the yellowness ofthe resin, preform and container. The preferred range of Co for blendscontaining 1 to 10 wt-% partially aromatic polyamide and 0.1 to 2.0mol-% of an ionic compatibilizer is 20 to 500 ppm.

Although not required, additives may be used in the polyester/polyamideblend. Conventional known additives include, but are not limited to anadditive of a dye, pigment, filler, branching agent, reheat agent,anti-blocking agent, antioxidant, anti-static agent, biocide, blowingagent, coupling agent, flame retardant, heat stabilizer, impactmodifier, UV and visible light stabilizer, crystallization aid,lubricant, plasticizer, processing aid, acetaldehyde and otherscavengers, and slip agent, or a mixture thereof.

The blend of polyester, ionic compatibilizer, cobalt salt and partiallyaromatic polyamide is conveniently prepared by adding the components arethe throat of the injection molding machine that produces a preform thatcan be stretch blow molded into the shape of the container. If aconventional polyester base resin designed for polyester containers isused, then one method is to prepare a master batch of a polyestercontaining the ionic compatibilizer, and optionally a transition metalcatalyst for active scavenging, together with the partially aromaticpolyamide using a gravimetric feeder for the three components.Alternatively the polyester resin can be polymerized with the ioniccompatibilizer, and optionally a transition metal catalyst for activescavenging, to form a copolymer. This copolymer can be mixed at theinjection molding machine with the partially aromatic nylon. Alternativeall the blend components can be blended together, or as a blend ofmaster batches, and fed as a single material to the extruder. The mixingsection of the extruder should be of a design to produce a homogeneousblend. This can be determined by measuring the thermal properties of thepreform and observing a single glass transition temperature in contrastto two separate glass transition temperatures of the partially aromaticpolyamide and polyester.

These process steps work well for forming carbonated soft drink, wateror beer bottles, and containers for hot fill applications, for example.The present invention can be employed in any of the conventional knownprocesses for producing a polyester container.

Testing Procedures

1. Oxygen and Carbon Dioxide Permeability of Films, Passive

Oxygen flux of film samples, at zero percent relative humidity, at oneatmosphere pressure, and at 25° C. was measured with a Mocon Ox-Tranmodel 2/20 (MOCON Minneapolis, Minn.). A mixture of 98% nitrogen with 2%hydrogen was used as the carrier gas, and 100% oxygen was used as thetest gas. Prior to testing, specimens were conditioned in nitrogeninside the unit for a minimum of twenty-four hours to remove traces ofatmospheric oxygen dissolved in the PET matrix. The conditioning wascontinued until a steady base line was obtained where the oxygen fluxchanged by less than one percent for a thirty-minute cycle.Subsequently, oxygen was introduced to the test cell. The test endedwhen the flux reached a steady state where the oxygen flux changed byless than 1% during a 30 minute test cycle. Calculation of the oxygenpermeability was done according to a literature method for permeationcoefficients for PET copolymers, from Fick's second law of diffusionwith appropriate boundary conditions. The literature documents are:Sekelik et al., Journal of Polymer Science Part B: Polymer Physics,1999, Volume 37, Pages 847-857. The second literature document isQureshi et al., Journal of Polymer Science Part B: Polymer Physics,2000, Volume 38, Pages 1679-1686. The third literature document isPolyakova, et al., Journal of Polymer Science Part B: Polymer Physics,2001, Volume 39, Pages 1889-1899.

The carbon dioxide permeability of films was measured in the samemanner, replacing the oxygen gas with carbon dioxide and using the MoconPermatran-C 4/40 instrument.

All film permeability values are reported in units of(cc(STP)·cm)/(m²·atm·day)).

2. Oxygen Permeability of Films, Active Scavenger.

The same method was used as for passive oxygen permeability above withthe exception that the oxygen flux did not necessarily equilibrate to asteady state. After the introduction of the oxygen into the cell, thereduction in the amount of oxygen was measured from 0 to at least 350hours. Treatment of the data generated an Apparent PermeationCoefficient (APC), as a function of time with oxygen exposure(cc(STP)·cm)/(m²·atm·day). The generated APC data is not a steady statevalue in normal permeation coefficients. APC is data generated thatdescribes oxygen permeation at a fixed point in time, even though thiscoefficient is changing slowly with time. These changes are too small tobe detected during the time necessary for measuring their value at anyfixed point in time. Calculation of the APC was done according to aliterature method for permeation coefficients for PET copolymers, fromFick's second law of diffusion with appropriate boundary conditions, inthe same manner as described for passive barrier permeability.

3. Carbon Dioxide Permeability of Bottles.

Carbon dioxide permeability of bottles was measured using a MOCONPermatran C-200 CO₂ Permeation System. Tests were conducted at 22° C.The bottles were purged with nitrogen and then pressurized with CO₂ at apressure of 60 psi (4.01 MPa). The bottles were left in ambientconditions for 3 days and the pressure measured. Bottles in which thepressure had dropped below 56 psi (3.75 Mpa) were rejected, otherwisethe bottles were repressurized to 60 psi (4.01 MPa) and placed in thetesting chamber, which has been purged with nitrogen for at least 5hours. After a day, measurements of the CO₂ in the test chamber weretaken over a 30 minute time frame, over an eight hour time period. Thenitrogen flow rate to the sensor was 100 cm³/min, and to the carrierstream was 460 cm³/min. Results are reported as cm³/bottle/day.

4. Intrinsic Viscosity (IV)

Intrinsic viscosity (IV) is determined by dissolving 0.2 grams of anamorphous polymer composition in 20 milliliters of dichloroacetic acidat a temperature of 25° C. and using an Ubbelhode viscometer todetermine the relative viscosity (RV). RV is converted to IV using theequation: IV=[(RV−1)×0.691]+0.063.

5. Color

The haze of the preform and bottle walls was measured with a Hunter LabColorQuest II instrument. D65 illuminant was used with a CIE 1964 10°standard observer. The haze is defined as the percent of the CIE Ydiffuse transmittance to the CIE Y total transmission. The color of thepreform and bottle walls was measured with the same instrument and isreported using the CIELAB color scale, L* is a measure of brightness, a*is a measure of redness (+) or greenness (−) and b* is a measure ofyellowness (+) or blueness (−).

6. Diethylene Glycol (DEG)

The DEG (diethylene glycol) content of the polymer is determined byhydrolyzing the polymer with an aqueous solution of ammonium hydroxidein a sealed reaction vessel at 220±5° C. for approximately two hours.The liquid portion of the

The DEG (diethylene glycol) content of the polymer is determined byhydrolyzing the polymer with an aqueous solution of ammonium hydroxidein a sealed reaction vessel at 220±5° C. for approximately two hours.The liquid portion of the hydrolyzed product is then analyzed by gaschromatography. The gas chromatography apparatus is a FID Detector(HP5890, HP7673A) from Hewlett Packard. The ammonium hydroxide is 2.8 to30% by weight ammonium hydroxide from Fisher Scientific and is reagentgrade.

7. Isophthalic and Naphthalene Dicarboxylic Acid

The percent isophthalic acid and naphthalene dicarboxylic acid presentin the amorphous polymer was determined at 285 nanometers using aHewlett Packard Liquid Chromatograph (HPLC) with an ultravioletdetector. An amorphous polymer sample was hydrolyzed in diluted sulfuricacid (10 ml acid in 1 liter deionized water) in a stainless steel bombat 230° C. for 3 hours. After cooling, an aqueous solution from the bombwas mixed with three volumes of methanol (HPLC grade) and an internalstandard solution. The mixed solution was introduced into the HPLC foranalysis.

8. Metal Content

The metal content of the ground polymer samples was measured with anAtom Scan 16 ICP Emission Spectrograph. The sample was dissolved byheating in ethanolamine, and on cooling, distilled water was added tocrystallize out the terephthalic acid. The solution was centrifuged, andthe supernatant liquid analyzed. Comparison of atomic emissions from thesamples under analysis with those of solutions of known metal ionconcentrations was used to determine the experimental values of metalsretained in the polymer samples.

9. Preform and Bottle Process

After solid state polymerization, the resin of the present invention istypically, dried for 4-6 hours at 170-180° C., melted and extruded intopreforms. Each preform for a 0.59 liter soft drink bottle, for example,employs about 24 grams of the resin. The preform is then heated to about100-120° C. and blown-molded into a 0.59 liter contour diameter giving astretch ratio of twelve (2×6). Since the bottle size is fixed, differentpreform sizes can be used for obtaining different stretch ratios.

10. Scanning Electron Micrograph

Films were prepared by compression molding by heating at 275° C. in apress for 3 minutes without pressure, then the pressure was cycledseveral times between 0 and 300 psi and then held at 300 psi for 4minutes. The film was quenched in ice water. These films were notchedwith a razor blade on the film surface to facilitate a brittle failure,immersed in liquid nitrogen for 15 minutes, removed and fractured byhand perpendicular to the thickness direction. Fracture surfaces werecoated with 100 angstrom of gold and were observed using a JEOL 840Ascanning electron microscope.

The following examples are given to illustrate the present invention,and it shall be understood that these examples are for the purposes ofillustration and are not intended to limit the scope of the invention.

EXAMPLES

Various polyester (PET) resins reflecting typical commercial recipeswere produced. Comonomers included isophthalic acid (or its dimethylester) (IPA) and diethylene glycol (DEG) as crystallization retardantsand naphthalene dicarboxylic acid (or its dimethyl ester) (NDC) toimprove the temperature at which a container can be filled.

Amorphous polyester was first produced with an IV of about 0.6, this wasthen solid phase polymerized to the final resin IV. The additives usedwere, manganese acetate, zinc acetate, cobalt acetate, antimony trioxideand poly-phosphoric acid. The analyses of these resins are set forth inTable 1.

TABLE 1 Resin Identification A B C D Process TA DMT DMT DMT IV 0.83 0.820.84 0.81 IPA, wt-% 2.5 3.1 0 0 NDC, wt-% 0 0 5 5 DEG, wt-% 1.5 0.7 0.60.6 Cobalt, ppm 30 40 100 0

A series of copolyesters were made containing various amounts of5-sulfoisophthalic acid (SIPA), either the ester or the gylcolate ofSIPA was used. The melt phase polymerization was conducted in the normalway, but the amorphous resin was not solid state polymerized for resinS3. In the case of Resin S1, zinc acetate was used in place of manganeseacetate as the ester-interchange catalyst. The analyses of these resinsare set forth in Table 2.

TABLE 2 Resin Identification S1 S2 S3 Process DMT DMT DMT IV 0.84 0.820.56 SIPA, mol-% 0.11 1.3 1.7 Cobalt, ppm 0 0 40

A master batch of the cobalt salt to be used as the transition metalcatalyst for active oxygen scavenging was made by late addition of 2wt-% cobalt octoate to a polyester prepared using 75 ppm Zn (as zincacetate), 250 ppm Sb (as antimony trioxide, 60 ppm P (as poly-phosphoricacid) and 2.5 wt-% IPA. This material had an IV of 0.35-0.40.

60 ppm P (as poly-phosphoric acid) and 2.5 wt-% IPA. This material hadan IV of 0.35-0.40.

Unless otherwise stated the partially aromatic nylon used in the blendwas Type 6007 from Mitsubishi Gas Chemical, Tokyo Japan. Type 6007 has anumber average molecular weight of 25, 900 and its melt viscosity at271° C. and 1000 sec⁻¹ is 280 Pa·s.

Unless otherwise stated the preforms were prepared on an Arburginjection molding machine using 24 g of material, and blown into a 0.59liter contour bottle on a Sidel SBO2 stretch blow molding machine. Thebottle sidewall thickness is about 0.25 mm.

Example 1

The effect of the interaction of SIPA with Co on the yellowness ofpreforms and bottles was studied by blending either polyester resin D orS1 with the cobalt master batch and MXD6. The yellowness value (b*) ofthe preforms and bottle sidewalls are set forth in Table 3 (lower ornegative b* values correspond to less yellowness).

TABLE 3 Pre- Bot- Run Co, MXD6, SIPA, form tle No. Resin ppm wt-% mol-%b* Delta¹ b* Delta² 1 D 0 0 0 11 Control 3.6 Control 2 D 0 5 0 19.3 8.37.1 3.5 3 D 100 0 0 0.7 −10.3 1 −2.6 4 D 200 5 0 4.2 −6.8 3.5 −0.1 5 S10 0 0.11 16.3 Control 4.6 Control 6 S1 0 5 0.11 17.5 1.2 5.5 0.9 7 S1100 0 0.11 −0.8 −17.1 1.1 −3.5 8 S1 200 5 0.11 −6.6 −22.9 2 −2.6¹Difference in b* of the preform compared to the control. ²Difference inb* of the bottle compared to the control.0.11 mol-% SIPA, there is a synergistic effect and the Co salt ismarkedly more effective in offsetting the yellowness.

Example 2

A similar trial was conducted using resin C as the control and theresults set forth in Table 4.

TABLE 4 Run MXD6, SIPA, Preform No. Resin Co, ppm wt-% mol-% b* Bottleb* 9 C 100 0 0 −0.1 1.2 10 C 200 5 0 3.6 5.7 11 S1 200 5 0.11 −3.5 3.6The haze of these preforms and bottle sidewalls are set forth in Table5.

TABLE 5 Run Co, Preform Bottle No. Resin ppm MXD6, wt-% SIPA, mol-%haze, % haze, % 9 C 100 0 0 9.5 1.3 10 C 200 5 0 16.4 13.9 11 S1 200 50.11 14.3 8.2

The results again show the synergistic effect of the ioniccompatibilizer on the cobalt salt as a means to reduce yellowness, inaddition the ionic compatibilizer reduced the haze of the bottlesidewall containing 5 wt-% MXD6.

Example 3

Another trial was conducted in which the amount of MXD6 was varied at aconstant SIPA level of 0.11 mol-%, and the results set forth in Table 6

TABLE 6 Run Co, Preform Bottle No. Resin ppm MXD6, wt-% SIPA, mol-% b*b* 12 C 100 0 0 0.4 0.8 13 S1 100 0 0.11 −1.8 1.1 14 C 200 3 0 1.4 2.415 S1 200 3 0.11 −7.4 1.9 16 C 200 4 0 1.0 2.8 17 S1 200 4 0.11 −7.8 2.018 C 200 5 0 3.2 3.2 19 S1 200 5 0.11 −6.1 2.6

At all levels of MXD6 the incorporation of an ionic compatibilizerreduced the yellowness.

The oxygen permeability of the bottle sidewalls was measured and theresults plotted in FIG. 1. This shows that the ionic compatibilizerdecreases the permeability at each MXD6 concentration. Surprisinglythere is a non-linear relationship of oxygen permeability with MXD6concentration with extremely low values at 5 wt-% MXD6.

Example 4

In order to better define the oxygen permeability as a function of MXD6concentration a series of blends were prepared using polyester A as thebase resin. The concentration of MXD6 used was 1, 2, 3, 4, 4.5 and 5wt-%, each containing 100 ppm cobalt octoate. The oxygen permeability ofthe bottle sidewalls was measured and the results shown in FIG. 2.

This illustrates that there is a surprising reduction in oxygenpermeability between 4.5 and 5 wt-% MXD6.

Example 5

Another trial was run in which the level of MXD6 was held constant at 5wt-% and the concentration of SIPA changed, the results are set forth inTable 7. In these runs the base polyester resin was A and the masterbatch of SIPA polymer S2 was used.

TABLE 7 Run Co, MXD6, Preform No. Resins ppm wt-% SIPA, mol-% b* Bottleb* 20 A 30 0 0 3.8 1.0 21 A 130 5 0 0.5 4.1 22 A/S2 130 5 0.13 −2.5 3.623 A/S2 130 5 0.26 −2.9 3.7 24 A/S2 130 5 0.65 −3.6 3.3 25 S2 100 5 1.3−9.1 2.8

These results show that the ionic compatibilizer can be used as a masterbatch to obtain the synergistic reduction of yellowness with cobalt, aswell as a copolymer that was used in the previous Examples 1-3.

Example 6

Instead of using sodium as the SIPA salt, a copolyester using thedivalent zinc ester was made using the process that was used forcopolymer S1. Since this Zn copolyester was more yellow than S1 nocomparison of the relative difference between Na-SIPA and Zn-SIPA can begiven. However the haze of bottle sidewalls made with PET resin A as thecontrol, using 0.11 mol-% SIPA (the runs containing MXD6 contained 100ppm Co) are compared in Table 8 below.

TABLE 8 Run No. MXD6, wt-% SIPA type Haze, % 26 0 none 5.5 27 5 none14.2 28 5 Na 12.0 29 5 Zn 9.6

It would appear that the divalent ionic compatibilizer is more effectivethan the monovalent in reducing the bottle sidewall haze.

Example 7

A low molecular weight MXD6 was prepared. A mixture of 438 g of adipicacid, 428.4 g of m-xylylenediamine and 500 g of deionized water werecharged in a 2-liter autoclave under nitrogen atmosphere. The mixturewas stirred for 15 minutes then heated to reflux for 30 minutes. Waterwas distilled off and the temperature was increased to 275° C. over aperiod of 60-90 minutes. The mixture was stirred at 275° C. for 30minutes before extrusion. This polymer had a viscosity of 9.5 Pa·s at1000 sec⁻¹ and 271° C. (compared to 280 Pa·s for the commercial 6007).

The procedure of Example 3 was followed, using this low molecular weightMXD6 (LMW) compared to the commercial 6007. The results are set forth inTable 9.

TABLE 9 Run Co, MXD6 MXD6, SIPA, Preform No. Resin ppm type wt-% mol-%b* Bottle b* 32 C 200 6007 3 0 2.0 2.5 33 C 200 LMW 3 0 3.4 2.1 34 C 2006007 5 0 4.2 3.5 35 C 200 LMW 5 0 1.1 3.6 36 S1 200 6007 5 0.11 −6.1 2.637 S1 200 LMW 5 0.11 −6.6 2.0This illustrates that the color is better (less yellow) with the lowmolecular weight MXD6 than 6007.

The haze of these runs was also measured and the results set forth inTable 10 below.

TABLE 10 Run Co, MXD6 MXD6, SIPA, Preform Bottle No. Resin ppm Type wt-%mol-% Haze, % Haze, % 32 C 200 6007 3 0 50.3 10.9 33 C 200 LMW 3 0 48.37.7 34 C 200 6007 5 0 50.1 14.0 35 C 200 LMW 5 0 49.9 11.8 36 S1 2006007 5 0.11 49.3 11.1 37 S1 200 LMW 5 0.11 45.4 7.4The use of the lower molecular MXD6 in conjunction with SIPA markedlyreduces the haze of the bottle sidewalls.

Example 7

In order to determine the effect of the ionic compatibilizer on MXD6domain size, a series of films were prepared and fractured. PET resin Bwas used together with blends with the S3 SIPA copolyester and 6007MXD6. The domain size was measured and the results set forth in Table11.

TABLE 11 MXD6, wt-% SIPA, mol-% Domain size, μm 10 0 0.8-1.5 20 02.2-4.5 20 1.35 0.2-0.5 10 0.03 0.5-1.5 10 0.08 0.5-1.5 10 0.16 0.2-0.5

This shows that at a low level of SIPA, less than 0.2 mol-%, the domainsize of a blend containing 10 wt-% MXD6 is reduced to less than 0.5 μm.

Example 8

A series of bottles were produced using C as the base PET resin, the S3SIPA copolyester and 6007 MXD6. The passive oxygen permeability, at 0%Relative Humidity, of the bottle sidewalls was measured and the resultsset forth in Table 12.

TABLE 12 O₂ Permeability (cc(STP) · cm)/ Run No. MXD6, wt-% SIPA, mol-%(m² · atm · day) 38 0 0 0.180 39 2.5 0 0.181 40 2.5 0.3 0.164 41 5 00.138 42 5 0.3 0.131 43 5 0.6 0.145 44 10 0 0.079 45 10 0.3 0.054 46 100.6 0.051This shows that the ionic compatibilizer is improving the oxygen gasbarrier at a given MXD6 level, possibly due to the reduction in domainsize, which increases the number of domains, as shown in Example 7.

Example 9

Following the procedure of Example 7 a polyamide was produced in which12% of the adipic acid was replaced with isophthalic acid. The meltviscosity of this polyamide at 171° C. and 1000 sec⁻¹ was 237 Pa·s. Thispolyamide was blended at a 5 wt-% level with PET resin C and ioniccompatibilizer S3 to give a level of SIPA of 0.6 mol-% in the blend.Bottles were prepared from this blend and the oxygen permeation ratemeasures at 0.155 (cc(STP)·cm)/(m²·atm·day). This can be compared with alower oxygen permeation rate of 0.145 measured on run 43 achieved with 5wt-% MXD6.

Example 10

The carbon dioxide transmission rate of 0.5 liter bottles made from PETresin A were measured to be 8.6 cc/bottle/day. The addition of 5 wt-%MXD6 decreased this rate to 4.5 cc/bottle/day.

Example 11

Master batches using cobalt stearate and cobalt naphthenate in place ofcobalt octoate were prepared using the same method as described abovefor cobalt octoate. Using PET base resin D, bottles were prepared usingdifferent amounts of MXD6 and different concentrations of cobaltoctoate, cobalt stearate and cobalt naphthenate. The bottle wall oxygenpermeability was measured and the value after 100 hours (at this timethe rate is at equilibrium, see FIG. 1) is set forth in Table 13.

TABLE 13 Oxygen Permeability @ 100 hours, MXD6, (cc(STP) · cm)/ Run No.wt-% Cobalt salt Co, ppm (m² · atm · day) 47 0 — — 0.150 48 1.75 Octoate200 0.098 49 1.75 Octoate 400 0.120 50 1.75 Stearate 100 0.098 51 1.75Stearate 200 0.122 52 3.0 Octoate 400 0.120 53 3.0 Octoate 60 0.048 545.0 Octoate 100 0.005 55 5.0 Stearate 30 0.005 56 5.0 Stearate 50 <0.00557 5.0 Naphthenate 50 <0.005An excess of the transition metal catalyst can in fact act as ananti-oxidant and increase the oxygen permeability, compare runs 48 and49, runs 52 and 53.

Although particular embodiments of the invention have been described indetail, it will be understood that the invention is not limitedcorrespondingly in scope, but include all changes and modificationscoming within the spirit and terms of the claims appended hereto.

1. A composition for containers comprising: a copolyester comprising ametal sulfonate salt; a partially aromatic polyamide; and a cobalt salt.2. The composition of claim 1, wherein said partially aromatic polyamideis present in a range from about 1 to about 10 wt. % of saidcomposition.
 3. The composition of claim 2, wherein said metal sulfonatesalt is present in a range from about 0.1 to about 2.0 mole % of saidcomposition.
 4. The composition of claim 1, wherein said cobalt salt ispresent in a range from about 20 to about 500 ppm of said composition.5. The composition of claim 1, wherein said partially aromatic polyamideis meta-xylylene adipamide.
 6. The composition of claim 1, wherein saidpartially aromatic polyamide is selected from the group consisting ofpoly(hexamethylene isophthalamide), poly(hexamethyleneadipamide-co-isophthalamide), poly(hexamethyleneadipamide-co-terephthalamide), poly(hexamethyleneisophthalamide-co-terephthalamide), and mixtures of two or more ofthese.
 7. The composition of claim 1, wherein said cobalt salt isselected from the group consisting of cobalt acetate, cobalt carbonate,cobalt chloride, cobalt hydroxide, cobalt naphthenate, cobalt oleate,cobalt linoleate, cobalt octoate, cobalt stearate, cobalt nitrate,cobalt phosphate, cobalt sulfate, cobalt (ethylene glycolate), andmixtures of two or more of these.
 8. The composition of claim 1, whereinthe metal ion of the metal sulfonate salt is selected from the groupconsisting of Na+, Li+, K+, Zn++, Mn++, and Ca++.
 9. The composition ofclaim 8, wherein said metal sulfonate salt is attached to an aromaticacid nucleus selected from the group consisting of sulfophthalic acid,sulfoterephthalic acid, sulfoisophthalic acid,4-sulfonaphthalene-2,7-dicarboxylic acid, and esters of each.
 10. Thecomposition of claim 1, wherein said metal sulfonate salt is5-sodiumsulfoisophthalic acid, 5-zincsulfoisophthalic acid, or dialkylesters thereof.
 11. The composition of claim 10, wherein the dialkylester is a dimethyl ester (SIM) or a glycol ester (SIPEG).
 12. Anarticle comprising the composition of any one of claims 1-11; whereinsaid article is a preform or a container.
 13. The article of claim 12,wherein the article is a container having an oxygen permeation rate of<0.01 cc(STP)-cm/m²-atm-day after 100 hours in oxygen.
 14. The containerof claim 13, having a yellowness value (b*) of less than 2.5.
 15. Thearticle of claim 12, wherein the article is a container that has acarbon dioxide transmission rate of less than 7 cc/bottle/day, based ona 0.59 liter bottle.